Luminous device

ABSTRACT

Provided is a means for improving the capability of injecting electrons from a cathode in a luminous element and solving problems about the production process thereof. In the present invention, a material having a smaller work function than a cathode material is used to form an inorganic conductive layer between the cathode and an organic compound layer. In this way, the capability of injecting electrons from the cathode can be improved. Furthermore, the film thereof can be thicker than that of a conventional cathode buffer layer formed by using an insulating material. Therefore, the film thickness can easily be controlled, and a decrease in production costs and an improvement in yield can be achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a luminous device using a luminouselement which has a film containing an organic compound (hereinafterreferred to as an “organic compound layer”) between a pair of electrodesand which can give fluorescence or luminescence by receiving an electricfield. The luminous device referred to in the present specification isan image display device, a luminescent device or a light source.Additionally, the following are included in examples of the luminousdevice: a module wherein a connector, for example, a flexible printedcircuit (FPC) or a tape automated bonding (TAB) tape, or a tape carrierpackage (TCP)) is set up onto a luminous element; a module wherein aprinted wiring board is set to the tip of a TAB tape or a TCP; and amodule wherein integrated circuits (IC) are directly mounted on aluminous element in a chip on glass (COG) manner.

2. Related Art

A luminous element is an element which emits light by receiving anelectric field. It is said that the luminescence mechanism thereof isbased on the following: by applying a voltage to an organic compoundlayer sandwiched between electrodes, electrons injected from the cathodeand holes injected from the anode are recombined in the organic compoundlayer to form molecules in an exciting state (hereinafter referred to as“molecular excimers”); and energy is radiated when the molecularexcimers return to the ground state thereof.

The kind of the molecular excimers which are made from the organiccompound may be a singlet exciting state excimer or a triplet excitingstate excimer. In the present specification, luminescence (that is,light emission) may be based on the contribution of any one of the two.

In such a luminous element, its organic compound layer is usually madeof a thin film having a thickness below 1 μm. The luminous element is aspontaneous light type element, wherein the organic compound layeritself emits light. Therefore, backlight, which is used in conventionalliquid crystal displays, is unnecessary. As a result, the luminouselement has a great advantage that it can be produced into a thin andlight form.

The time from the injection of carriers to the recombination thereof inthe organic compound layer having a thickness of about 100 to 200 nm isabout several tens nanoseconds in light of carrier mobility in theorganic compound layer. A time up to luminescence, which includes thestep from the recombination of the carrier to luminescence, is a time inorder of microseconds or less. Therefore, the luminous element also hasan advantage that the response thereof is very rapid.

Since a luminous element is of a carrier injection type, the luminouselement can be driven by DC voltage and noises are not easily generated.About driving voltage, a sufficient brightness of 100 cd/m² is attainedat 5.5 V by making an organic compound layer to a super-thin film havinga uniform thickness of about 100 nm, selecting an electrode material soas to make a carrier injection barrier against the organic compoundlayer small, and further introducing a hetero-structure (bilayerstructure) (document 1: C. W. Tang and S. A. VanSlyke, & quot; Organicelectroluminescent diodes & quot; Applied Physics letters, vol. 51, No.12, 913-915 (1987)).

In light of such properties such as thinness and lightness, high-speedresponse, and DC low voltage driving ability, attention is paid to aluminous element as a flat panel display element in the next generation.Since the luminous element is of a spontaneous light type and has a widefield angle, the luminous element is relatively easy to watch. Thus, itcan be considered that the luminous element is effective as an elementused in a display screen in portable devices.

In luminous devices formed by arranging such luminous elements in amatrix form, driving methods called passive matrix driving (simplematrix type) and active matrix driving (active matrix type) can be used.However, in the case in which the density of pixels increases, it isconsidered that the active matrix type wherein a switch is fitted toeach pixel (or each dot) is more profitable since lower voltage drivingcan be attained.

Incidentally, in such a luminous element, a metal material having a lowwork function is used as a cathode since electron injection isfacilitated. Hitherto, the following have been investigated as materialssatisfying practical properties: magnesium alloy such as alloy of Mg andAg, and aluminum alloy such as alloy of Al and Li. All of the materialsystems are easily oxidized by water content in the atmosphere, so thata dark spot, which is a luminescence defect of the element, is generatedor a rise in voltage occurs. Therefore, a form using some protectivefilm or some sealing structure is necessary as a final form of theelement.

In light of the background art of the above-mentioned alloy electrodes,it has been desired to develop more stable cathodes. In recent years, ithas been reported that by interposing a cathode buffer layer made oflithium fluoride (LiF) or the like as a super-thin insulating layer (0.5nm), even an aluminum cathode can give luminescence property equivalentto or more than that of alloy of Mg and Ag, or the like alloy (document2: L. S. Hung, C. W. Tang and M. G. Mason: Appl. Phys. Lett,. 70(2), 13Jan. (1997).

The mechanism of the property improvement by disposing this cathodebuffer layer would be as follows: when LiF constituting the cathodebuffer layer is formed to contact Alq₃ constituting an electrontransport layer of an organic compound layer, the energy band of Alq₃ isbent to lower an electron injection barrier.

As described above, in a luminous element composed of an anode, acathode and an organic compound layer, an invention is made forimproving the capability of injecting carriers from the electrode,resulting from an element characteristic of the luminous element.

Hitherto, a simple substance selected from elements belonging to the Igroup or the II group in the periodic table or a compound containingthis substance has been used as a material having a small work functionto form a cathode buffer layer between the cathode and the organiccompound layer.

However, in the case in which any metal selected from alkali metals andalkali earth metals belonging to the I group or the II group in theperiodic table is used alone for the cathode buffer layer, there arisesa problem that the metal diffuses to have a bad effect on properties ofa TFT connected to the luminous element.

On the other hand, in the case in which the compound containing anyelement selected from elements belonging to the I group or the II groupin the periodic table is used for the cathode buffer layer, a compoundof the element and oxygen, fluorine or the like belonging to the XVI orXVII group in the periodic table, which has a large electronegativity,is generally used in order to make work function smaller. However, sucha compound is non-conductive and thus electron-injection capability isimproved. However, in order that the element characteristic is notdeteriorated, it is necessary to make the film thickness of the cathodebuffer layer as highly thin as 1 nm or less. Therefore, a scattering inthe film thickness is easily generated in respective pixels, and it isdifficult to control the film thickness.

SUMMARY OF THE INVENTION

Thus, in order to solve the problems in the case in which a cathodebuffer layer is conventionally formed in the production of a luminouselement, an object of the present invention is to form a new layerinstead thereof so as to improve the capability of injecting electronsfrom a cathode and further to provide a means for solving the problemsin the production.

In the present invention, instead of a conventional cathode bufferlayer, the following is formed between a cathode and an organic compoundlayer: an inorganic conductive layer made of an inorganic compoundhaving a smaller work function than a cathode material and having anelectric conductivity.

The inorganic conductive layer formed in the present invention is formedusing a conductive inorganic compound comprising an element belonging tothe II group in the periodic table and having a smaller function than acathode material. In this way, an energy barrier between the cathode andthe organic compound layer can be relieved. Therefore, the capability ofinjecting electrons from the cathode can be improved.

By forming the inorganic conductive layer made of the inorganic compoundhaving an electric conductivity, a more stable compound, which mainlyhas a covalent bond, is used in the present invention when compared withthe case in which a cathode buffer layer made of a single substanceconsisting of an element belonging to the I or II group in the periodictable is used. Therefore, a problem of diffusion generated when thesingle element is used can be prevented. Luminescence can be moresufficiently obtained even if the inorganic conductive layer is madethicker in the present invention than in the case in which the cathodebuffer layer made of the insulating inorganic compound is formed.Therefore, the film thickness can easily be controlled, and a reductionin production costs and an improvement in yield can be achieved.

A first aspect of the present invention is a luminous device comprisingan anode, a cathode and an organic compound layer, the device furthercomprising a conductive film made of an inorganic compound formedbetween the organic compound layer and the cathode, wherein the organiccompound layer is formed to contact the anode, and the conductive filmis made of a material having a smaller work function than the cathodeand an electric conductivity of 1×10⁻¹⁰ S/m or more.

Since an inorganic compound used for a cathode buffer layer which isformed between a cathode and an organic compound layer generally has alow electric conductivity, the luminous element cannot give luminescencesufficiently if the film thickness thereof is not set to 1 nm or less.In the present invention, however, by using the inorganic compoundhaving an electric conductivity of 1×10⁻¹⁰ s/m or more for theconductive film, the film thickness thereof can be controlled. For thisreason, the formed luminous element can give sufficient luminescence.

A second aspect of the present invention is a luminous device comprisingan anode, a cathode and an organic compound layer, the device furthercomprising a conductive film made of an inorganic compound formedbetween the organic compound layer and the cathode, wherein the organiccompound layer is formed to contact the anode, and the conductive filmis made of a material having a work function of 3.5 eV or less and anelectric conductivity of 1×10⁻¹⁰ S/m or more.

Since the organic compound which makes the organic compound layer has asmaller electron affinity than metals and so on, it is necessary to usean electrode having a small work function as an electrode for improvingthe capability of injecting electrons. For example, —Mg:Ag alloy, whichhas been investigated as a cathode material satisfying practicalproperties so far, has a work function of 3.7 eV (document 3: M. A.Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest; Veryhigh-efficiency green organic light-emitting devices based onelectrophosphorescence; Applied Physics Letters, vol. 75, No. 1, 4-6(1999)).

By forming the inorganic conductive film having a work function of 3.5eV or less between the cathode and the organic compound layer in thepresent invention, an energy barrier between the cathode and the organiccompound layer can be relieved even if the work function of the cathodeitself is not very small. Therefore, the capability of injectingelectrons from the cathode can be improved.

A third aspect of a luminous device comprising an anode, a cathode andan organic compound layer, the device further comprising a conductivefilm made of an inorganic compound formed between the organic compoundlayer and the cathode, wherein the organic compound layer is formed tocontact the anode, both of the cathode and the conductive film have athickness of 20 nm or less, and the conductive film is made of amaterial having a smaller work function than the cathode and an electricconductivity of 1×10⁻¹⁰ S/m or more.

A fourth aspect of the present invention is a luminous device comprisingan anode, a cathode and an organic compound layer, the device furthercomprising a conductive film made of an inorganic compound formedbetween the organic compound layer and the cathode, wherein the organiccompound layer is formed to contact the anode, the cathode and theconductive film have a transmissivity of 70% or more, and the conductivefilm is made of a material having a smaller work function than thecathode and an electric conductivity of 1×10⁻¹⁰ S/m or more, so as tohave a thickness of 1 to 20 nm. The transmissivity means atransmissivity of visible rays being 70-100%.

A fifth aspect of the present invention is a luminous device comprisingan anode, a cathode and an organic compound layer, the device furthercomprising a conductive film made of an inorganic compound formedbetween the organic compound layer and the cathode, wherein the organiccompound layer is formed to contact the anode, both of the cathode andthe conductive film have a thickness of 20 nm or less, and theconductive film is made of a material having a work function of 3.5 eVor less and an electric conductivity of 1×10⁻¹⁰ S/m or more.

A sixth aspect of the present invention is a luminous device comprisingan anode, a cathode and an organic compound layer, the device furthercomprising a conductive film made of an inorganic compound formedbetween the organic compound layer and the cathode, wherein the organiccompound layer is formed to contact the anode the cathode and theconductive film have a transmissivity of 70% or more, and the conductivefilm is made of a material having a work function of 3.5 eV or less andan electric conductivity of 1×10⁻¹⁰ S/m or more, so as to have athickness of 1 to 20 nm.

In the above-mentioned aspects, the conductive film comprises oneelement or more than one element belonging to the II group in theperiodic table.

In the above-mentioned aspects, the conductive film is made of one ormore selected from nitrides, sulfides, borides or silicates comprisingan element belonging to the II group in the periodic table.

In the above-mentioned aspects, the conductive film comprises one ormore selected from calcium nitride, magnesium nitride, calcium sulfide,magnesium sulfide, strontium sulfide, barium sulfide, magnesium boride,magnesium silicate, calcium silicate, strontium silicate and bariumsilicate. In addition, in the above-mentioned aspects, the conductivefilm contains one or a plurality of materials selected from a boridecontaining a rare earth element. Further, in the above-mentionedaspects, the conductive film contains one or a plurality of materialsselected from the group consisting of lanthanum boride, yttrium borideand cerium boride.

In the above-mentioned aspects, the inorganic conductive layer is formedmainly by vapor deposition. In the case of high melting point materialsuch as a boride of rare earth element, it may be formed by sputtering.In the case in which sputtering is used to form the organic compoundlayer and subsequently form the inorganic conductive layer, it isdesired to dispose a barrier layer for preventing the damage of theorganic compound layer at the time of the sputtering. As the materialwhich makes the barrier layer, specifically copper phthalocyanine(referred to as Cu-Pc hereinafter) or the like can be used.

In the case in which a cathode buffer layer made of an insulatingmaterial is conventionally formed, the film thereof cannot be madethick. However, the above-mentioned present invention makes it possibleto make the film of the inorganic conductive layer thicker than that ofthe cathode buffer layer; therefore, the film thicknesses of respectivepixels can easily be controlled. As a result, problems about productionprocess can be solved.

The luminous device of the present invention may be an active matrixtype luminous device having luminous elements connected electrically toTFTs, or a passive matrix type luminous device.

The luminescence emitted from the luminous device of the presentinvention may be luminescence based on either of a singlet excitationstate or a triplet excitation state, or both of the two states.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views for explaining an element structure of aluminous device of the present invention.

FIGS. 2A to 2 c are views for explaining an element structure of aluminous device of the present invention.

FIGS. 3A and 3B are views for explaining an element structure of aluminous device of the present invention.

FIG. 4 is a view for explaining an element structure of a luminousdevice of the present invention.

FIGS. 5A to 5C are views for explaining a process of producing aluminous device of the present invention.

FIGS. 6A to 6C are views for explaining the process of producing theluminous device of the present invention.

FIGS. 7A and 7B are views for explaining the process of producing theluminous device of the present invention.

FIGS. 8A and 8B are views for explaining the process of producing theluminous device of the present invention.

FIGS. 9A to 9D are views for explaining an element structure of aluminous device of the present invention.

FIGS. 10A and 10B are a top view of a pixel section of a luminousdevice, and a sectional view thereof.

FIGS. 11A and 11B are views for explaining an element structure of aluminous device of the present invention.

FIGS. 12A and 12B are views for explaining a structure of a reversestagger type TFT.

FIG. 13 is a view for explaining a passive matrix type luminous device.

FIGS. 14A to 14H are views illustrating examples of electricalapparatus.

FIGS. 15A and 15B are graphs showing results obtained by measuring theelement characteristics of a conventional luminous element.

FIGS. 16A and 16B are graphs showing results obtained by measuring theelement characteristics of a conventional luminous element.

FIGS. 17A and 17B are graphs showing results obtained by measuring theelement characteristics of a luminous element of the present invention.

FIGS. 18A and 18B are graphs showing results obtained by measuring theelement characteristics of a luminous element of the present invention.

FIGS. 19A and 19B are graphs showing results obtained by measuring theelement characteristics of a luminous element of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference toFIGS. 1 and 2. A luminous device of the present invention comprises aluminous element having an element structure illustrated in FIG. 1A.

As illustrated in FIG. 1A, a cathode 102 is formed on a substrate 101,and an inorganic conductive layer 103 is formed to contact the cathode102.

The inorganic conductive layer 103 is made of a material having asmaller work function than the material of the cathode, and ispreferably made of a material having a work function of 3.5 eV or less.The inorganic conductive layer 103 is made of a material having anelectric conductivity of 1×10⁻¹⁰ μm or more. Since the inorganicconductive layer 103 in the present invention has electric conductivity,the film thereof can be thicker. It is however desired that the filmthickness is set to about 1 to 0.30 nm from the viewpoint of improvementin efficiency of taking out light.

Furthermore, an organic compound layer 104 is formed to contact theinorganic conductive layer 103. The organic compound layer 104 may beformed to have a monolayer structure of only a luminous layer or may beformed by combining a luminous layer with one or more layers havingdifferent actions onto carriers, such as a hole injection layer, a holetransport layer, a hole block layer, an electron transport layer and anelectron injection layer.

Next, an anode 105 is formed to contact the organic compound layer 104.

FIG. 1B shows an energy band in the luminous element having the elementstructure illustrated in FIG. 1A. The organic compound layer 104 formedbetween the cathode 102 and the anode 105 has an electron transportlayer 106, a luminous layer 107, a hole transport layer 108 and a holeinjection layer 109. They have a relationship about the magnitude ofwork functions as illustrated in FIG. 1B.

By forming the inorganic conductive layer 103 of the present inventionusing a material having an energy level between energy levels of theelectron transport layer 106 constituting a part of the organic compoundlayer 104 and the cathode 102, an energy barrier 110 generated whenelectrons are injected from the cathode 102 can be relieved. In thisway, the electron-injecting capability of the luminous element can beimproved.

In FIG. 1A, the element structure wherein the cathode 102 is formed tocontact the substrate 101 is illustrated. However, the present inventionis not limited to this structure, and a structure wherein an anode isformed to contact the substrate 101 may be adopted. In this case, thefollowing element structure is adopted: an element structure wherein theanode is formed to contact the substrate 101, an organic compound layeris formed to contact the anode, and an inorganic conductive layer isformed between the organic compound layer and the cathode.

The following will describe Embodiments 1 to 3 of an active matrix typeluminous device having the above-mentioned element structure, referringto FIG. 2.

Embodiment 1

A sectional structure of a pixel section of a luminous device will bedescribed as Embodiment 1 of the present invention, referring to FIG.2A.

In FIG. 2A, semiconductor elements are formed on a substrate 201. As thesubstrate 201, a glass substrate having transparency is used. However, aquartz substrate may be used. As the semiconductor elements, TFTs areused. An active layer in each of the TFTs has at least a channel formedregion 202, a source region 203 and a drain region 204.

The active layer in each of the TFTs is covered with a gate insulatingfilm 205, and a gate electrode 206 overlapping the channel formed region202 across the gate insulating film 205 is formed. An interlayerinsulating film 207 covering the gate electrode 206 is deposited, and anelectrode connected electrically to the source region or the drainregion of each of the TFTs is formed on the interlayer insulating film207. An electrode reaching a drain region 204 of a current-controllingTFT 222, which is an n-channel type TFT, becomes a cathode 208 of aluminous element. An insulating layer 209 having an opening to cover theedge portion of the cathode 208 and have a tapered edge is deposited. Aninorganic conductive layer 210 is formed on the cathode 208. An organiccompound layer 211 is deposited thereon. An anode 212 is formed on theorganic compound layer 211 to form a luminous element. The luminouselement is sealed up with a sealing substrate 214 in the state that aspace 213 remains.

In the present embodiment, the inorganic conductive layer 210 is formedto contact the cathode 208 connected electrically to the TFT, and theorganic compound layer 211 is formed to contact this layer 210.

Furthermore, the inorganic conductive layer 210 can be formed to have afilm thickness of 1 to 30 nm since the inorganic conductive layer 210has electric conductivity. Thus, it becomes easy to control the filmthickness.

In the present Embodiment 1, by using a transparent conductive film forthe anode 212, light generated by recombination of carriers in theorganic compound layer 211 can be emitted from the side of the anode212.

In the present Embodiment 1, the inorganic conductive layer 210 containsan element belonging to the II group in the periodic table, or containsa nitride, a sulfide, a boride or a silicate of this element. Theinorganic conductive layer 210 may contain a boride of rare earthelement.

Specifically, the inorganic conductive layer 210 can be made of thefollowing material: calcium nitride, magnesium nitride, calcium sulfide,magnesium sulfide, strontium sulfide, barium sulfide, magnesium boride,magnesium silicate, calcium silicate, strontium silicate, bariumsilicate, or the like. Besides, the inorganic conductive layer 210 canbe made of a boride containing rare earth element (Sc, Y, La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), preferably, lanthanumboride, yttrium boride and cerium boride. By using a stable compoundmainly having a covalent bond, it is possible to prevent the diffusionof impurity ions (typically, alkali metal ions or alkali earth metalions), which becomes a problem when a simple element of an alkali metalor an alkali earth metal is used. Thus, the capability of injectingelectrons from the cathode 208 can be improved.

The material for forming the organic compound layer 211 may be a knownhigh-molecular organic compound or a known low-molecular organiccompound.

In the present Embodiment 1, the organic compound layer 211 is formedand subsequently the anode 212 made of a transparent conductive film isformed by sputtering; therefore, it is preferred to form a barrier layer(not illustrated) for preventing the damage of the organic compoundlayer 211 when the anode 212 is formed. By forming the hole injectionlayer which constitutes one part of the organic compound layer 211, thehole injection layer can have the function of a barrier layer;therefore, the hole injection layer may be formed. For the holeinjection layer, copper phthalocyanine (hereinafter referred to asCu-Pc) can be used.

Herein, the TFT of a top gate type has been described as an example.However, the type of the TFT is not particularly limited, and thepresent invention may be applied to a bottom gate type TFT, a forwardstagger type TFT and the like type TFTs.

Embodiment 2

The following will describe a sectional structure of a pixel section ofa luminous device as Embodiment 2 of the present invention, referring toFIG. 2B. The structure formed until the interlayer insulating film 207is formed is the same as in Embodiment 1 except that thecurrent-controlling TFT is formed to be of a p-channel type. Thus,detailed description thereof is omitted.

On the interlayer insulating film 207 is formed an electrode connectedelectrically to the source region or the drain region of each of theTFTs. An electrode reaching a drain region 204 of a current-controllingTFT 222, which is a p-channel type TFT, is connected electrically to ananode 231 of the luminous element. An insulating layer 232 having anopening which covers the edge portion of the anode 231 and has a taperededge is deposited.

An organic compound layer 233 is deposited on the anode 231. Aninorganic conductive layer 234 is deposited thereon. A cathode 235 isset up on the inorganic conductive layer 234 to form the luminouselement. In the same manner as in Embodiment 1, the luminous element issealed up with a sealing substrate 214 in the state that a space 213remains.

In the present embodiment 2, the organic compound layer 233 is formed tocontact the anode 231 connected electrically to the TFT. The inorganicconductive layer 234 is formed between the organic compound layer 233and the cathode 235 to contact each of the two.

In the present Embodiment 2, by using a transparent conductive film forthe anode 231, light generated by recombination of carriers in theorganic compound layer 233 can be emitted from the side of the anode231. In the present Embodiment 2, light penetrating through the anode231 also penetrates through the substrate 201 so as to be emittedoutside. For this reason, it is necessary to use a transparent materialas a material used for the substrate 201. Specifically, a material suchas glass, quartz or plastic is used.

In the present Embodiment 2, the organic compound layer 233 is formedand subsequently the inorganic conductive layer 234 is formed bysputtering; therefore, it is allowable to form a barrier layer (notillustrated) for preventing the damage of the organic compound layer 233when the layer 234 is formed. For the barrier layer, Cu-Pc or the likemay be used.

Embodiment 3

The following will describe a sectional structure of a pixel section ofa luminous device as Embodiment 3 of the present invention, referring toFIG. 2C. The structure formed until the interlayer insulating film 207is formed is the same as in Embodiment 1 except that thecurrent-controlling TFT is formed to be of a p-channel type. Thus,detailed description thereof is omitted.

In the present Embodiment 3, a first electrode 241 is formed connectedelectrically to each TFT. A material for forming the first electrode 241is preferably any one selected from conductive materials havinglight-shading property and a high reflectivity, for example, aluminum,titanium, or tungsten. It is preferred to use a monolayer made of anyone selected from the above-mentioned conductive materials or alamination wherein two or more selected from the conductive materials.

A second electrode 242 made of a material having a large work functionis formed on the first electrode 241. It is desired to use a materialhaving a small work function, such as ITO. An insulating layer 243having an opening which covers the edge portion of the second electrode242 and has a tapered edge is deposited. In the present embodiment 3,the lamination composed of the first electrode having light shadingproperty and reflectivity and the second electrode having a small workfunction functions as an anode 244 of a single luminous element.

An organic compound layer 245 is deposited on the anode 244. Aninorganic conductive layer 246 is deposited thereon. A cathode 247 isset up on the inorganic conductive layer 246 to form the luminouselement. In the same manner as in Embodiment 1 and 2, the luminouselement is sealed up with a sealing substrate 214 in the state that aspace 213 remains.

The present embodiment 3 has the follow structure: the anode 244 isformed by stacking the first electrode 241 connected electrically to theTFT and the second electrode 242; the organic compound layer 245 isformed to contact the anode 244; and the inorganic conductive layer 246is formed between the organic compound layer 245 and the cathode 247 tocontact each of the two.

By adopting such a structure, luminescence generated by recombination ofcarriers in the organic compound layer 245 can be effectively emittedfrom the side of the cathode 247 without being emitted from the side ofthe anode 242.

In the present Embodiment 3, the inorganic conductive layer 246 isformed by sputtering after the formation of the organic compound layer245. It is therefore allowable to deposit a barrier layer (notillustrated) for preventing the damage of the organic compound layer 245when the layer 246 is formed. As the barrier layer, a material such asCu-Pc can be used.

In order to emit luminescence generated in the organic compound layer245 from the side of the cathode 247 in the present Embodiment 3, thefilm thickness of the inorganic conductive layer 246 is preferably setto 1 to 20 nm. Moreover, the cathode 247 is preferably formed to have afilm thickness of 1 to 20 nm in order to penetrate light through thecathode 247.

The following will describe the present invention having theabove-mentioned structure in more detail by way of Examples.

EXAMPLES

Examples of the present invention will be described.

Example 1

In the present Example, luminous devices having the element structuresin Embodiments 1, 2 and 3 will be described in detail.

FIG. 3A illustrates a structure of the luminous element described inEmbodiment 1. That is, this structure is a structure wherein aninorganic conductive layer 302 is formed on a cathode 301, an organiccompound layer 303 is formed on the inorganic conductive layer 302, andan anode 307 is formed on the organic compound layer 303, and is anupward light-emitting type element structure wherein light generatedfrom the organic compound layer 303 penetrates outside through the anode307. In the case of this element structure, the ITO film, which is atransparent conductive film, is formed on the organic compound layer 303by sputtering. Therefore, in order to prevent the damage of the organiccompound layer 303 at the time of the sputtering, it is desired to setup a barrier layer 306 formed by vapor deposition.

As illustrated in FIG. 2A, the cathode 301 is an electrode connectedelectrically to the current-controlling TFT 222, and is made of Al tohave a thickness of 120 nm in the present example.

The inorganic conductive layer 302 on the cathode 301 is made by vapordeposition using CaN, to have a thickness of 30 nm.

In the present example, the organic compound layer 303 formed on theinorganic conductive layer 302 has a lamination structure of a luminouslayer 304 and a hole transport layer 305. The organic compound layer 303in the present example will be described about a case in which the layer303 is made of a high-molecular organic compound. However, the layer 303may be made of a monolayer or a multilayer of a low-molecular compound.

The luminous layer 304 can be made of a material of poly p-phenylenevinylene, poly p-phenylene, polythiophene, or polyfluorene type.

As the poly p-phenylene vinylene type material, the following can beused: poly(p-phenylene vinylene), referred to as PPV hereinafter, orpoly[2-(2′-ethylhexoxy)-5-methoxy-1,4-phenylene vinylene], referred toas MEH-PPV hereinafter, each of which can give orange luminescence;poly[2-(dialkoxyphenyl)-1,4-phenylene vinylene], referred to asROPh-PPV, which can give green luminescence; or the like.

As the polyparaphenylene type material, the following can be used:poly(2,5-dialkoxy-1,4-phenylene), referred to as RO—PPP hereinafter,poly(2,5-dihexoxy-1,4-phenylene), each of which can give blueluminescence; or the like.

As the polythiophene type material, the following can be used:poly(3-alkylthiophene), referred to as PAT hereinafter,poly(3-hexylthiophene), referred to as PHT hereinafter,poly(3-cyclohexylthiophene), referred to as PCHT hereinafter,poly(3-cyclohexyl-4-methylthiophene), referred to as PCHMT hereinafter,poly(3,4-dicyclohexylthiophene), referred to as PDCHT hereinafter,poly[3-(4-octylphenyl)-thiophene], referred to as POPT hereinafter, orpoly[3-(4-octylphenyl)-2,2-bithiophene], referred to as PTOPThereinafter, each of which can give red luminescence; or the like.

As the polyfluorene type material, the following can be used:poly(9,9-dialkylfluorene), referred to as PDAF hereinafter, orpoly(9,9-dioctylfluorene), referred to as PDOF hereinafter, each ofwhich can give blue luminescence; or the like.

The above-mentioned material which can form a luminous layer isdissolved in an organic solvent, and then the solution is applied by anycoating method. Examples of the organic solvent used herein includetoluene, benzene, chlorobenzene, dichlorobenzene, chloroform, tetralin,xylene, dichloromethane, cyclohexane, NMP (N-methyl-2-pyrrolidone),dimethylsulfoxide, cyclohexanone, dioxane, and THF (tetrahydrofuran).

The hole transport layer 305 can be formed using both ofpoly(3,4-ethylene dioxythiophene), referred to as PEDOT hereinafter, andpolystyrene sulfonic acid, referred to as PSS hereinafter, which is anacceptor material, or both of polyaniline, referred to as PANIhereinafter, and a camphor sulfonic acid, referred to as CSAhereinafter. The material is made into an aqueous solution since thematerial is water-soluble, and then the aqueous solution is applied byany coating method so as to form a film.

In the present example, a film made of PPV is formed as the luminouslayer 304 to have a thickness of 80 nm, and a film composed of PEDOT andPSS is formed as the hole transport layer 305 to have a thickness of 30nm.

A barrier layer 306 is formed on the organic compound layer 303. As thematerial which makes the barrier layer 306, there can be used a materialhaving a large work function, such as gold or silver, Cu-Pc or the like.In the present example, Au is used to form the barrier layer 303 of 20nm thickness by vapor deposition.

Next, an anode 307 is formed. As the material which makes the anode 307,a transparent material such as ITO (indium tin oxide) or IZO (indiumzinc oxide) is used. In the present example, ITO is used to form theanode 397 of 110 nm thickness by sputtering.

As described above, an upward light-emitting type luminous elementdescribed in Embodiment 1 can be obtained.

The structure of the luminous element described in Embodiment 2 isillustrated in FIG. 3B. That is, this structure is a structure whereinan organic compound layer 312 is formed on an anode 311, an inorganicconductive layer 316 is formed on the organic compound layer 312 and acathode 317 is formed thereon, and is a downward light-emitting elementstructure, wherein light generated in the organic compound layer 312penetrates outside through the anode 311.

As illustrated in FIG. 2B, the anode 311 is a transparent electrodeconnected electrically to the current-controlling TFT 222, and is madeof ITO to have a thickness of 110 nm in the present example.

The organic compound layer 312 formed on the anode 311 has a laminationstructure of a hole transport layer 313 and a luminous layer 314 asillustrated in FIG. 3A. As the materials which make the hole transportlayer 313 and the luminous layer 314, the same materials as describedabove can be used. In the same manner as illustrated in FIG. 3A, thehole transport layer 313 composed of PEDOT and PSS is formed to have athickness of 30 nm, and the luminous layer 314 made of PPV is formed tohave a thickness of 80 nm.

The inorganic conductive layer 316 on the organic compound 312 is formedby vapor deposition using CaN, to have a thickness of 30 nm in the sameway as illustrated in FIG. 3A.

A cathode 317 is formed on the inorganic conductive layer 316. Thecathode 317 is formed using Al as the material of the cathode herein, tohave a thickness of 120 nm.

As described above, a downward light-emitting type luminous elementdescribed in Embodiment 2 can be obtained.

The structure of the luminous element described in Embodiment 3 isillustrated in FIG. 4. That is, this structure is a structure wherein anorganic compound layer 402 is formed on an anode 401, an inorganicconductive layer 406 is formed on the organic compound layer 402, and acathode 407 is formed thereon, and is an upward light-emitting elementstructure, wherein light generated in the organic compound layer 402penetrates outside through the inorganic conductive layer 406 and thecathode 407.

As illustrated in FIG. 2C, the anode 401 is made of a lamination of afirst electrode 241 and a second electrode 242 connected electrically tothe current-controlling TFT 222. In the present example, the anode 401is made of a lamination of Al which makes the first electrode 241 havinga thickness of 100 nm and ITO which makes the second electrode 242having a thickness of 50 nm.

The organic compound 402 formed on the anode 401 is made of a laminationof a hole transport layer 403 and a luminous layer 404 in the samemanner as illustrated in FIG. 3A. The materials which make the holetransport layer 403 and the luminous layer 404 can be selected from theabove-mentioned materials, and used. In the same manner as illustratedin FIG. 3A, the hole transport layer 403 composed of PEDOT and PSS isformed to have a thickness of 30 nm, and the luminous layer 404 made ofPPV is formed to have a thickness of 80 nm.

In the same manner as illustrated in FIG. 3A, the inorganic conductivelayer 406 formed on the organic compound layer 402 is formed by vapordeposition using CaN. The inorganic conductive layer 406 is formedherein to have a thickness of 10 nm in such a manner that lightgenerated in the organic compound layer 402 can penetrate through theinorganic conductive layer 406.

A cathode 407 is formed on the inorganic conductive layer 406. Al isused herein as the material of the cathode to form the cathode 407 tohave a thickness of 20 nm, considering light transmissivity.

As described above, an upward light-emitting luminous element describedin Embodiment 3 can be obtained.

Example 2

In forming a element substrate, a method of simultaneously forming, onthe same substrate, a pixel portion and TFTs (n-channel TFT andp-channel TFT) of a driver circuit formed in the periphery of the pixelportion and forming a luminescent element which connect to the TFT atpixel portion is described in detail using FIGS. 5 to 8 in this example.Note that, in this example, luminescent element having the structuredescribed in example 1 is formed.

First, in this example, a substrate 600 is used, which is made fromglass, such as barium borosilicate glass or aluminum borosilicate,represented by such as Corning #7059 glass and #1737. Note that, as thesubstrate 600, a quartz substrate on which an insulating film is formed,may be used as the replace. A plastic substrate having heat resistanceto a process temperature of this example may also be used.

Then, a base film 601 formed from an insulating film such as a siliconoxide film, a silicon nitride film or a silicon oxynitride film. In thisexample, a two-layer structure is used as the base film 601. However, asingle-layer film or a lamination structure consisting of two or morelayers of the insulating film may be used. As a first layer of the basefilm 601, a silicon oxynitride film 601 a is formed into a thickness of10 to 200 nm (preferably 50 to 100 nm) using SiH₄, NH₃, and N₂O asreaction gases by plasma CVD. In this example, the silicon oxynitridefilm 601 a (composition ratio Si=32%, O=27%, N=24% and H=17%) having afilm thickness of 50 nm is formed.

Then, as a second layer of the base film 601, a silicon oxynitride film601 b is formed so as to laminate thereon into a thickness of 50 to 200nm (preferably 100 to 150 nm) using SiH₄ and N₂O as reaction gases byplasma CVD. In this example, the silicon oxynitride film 601 b(composition ratio Si=32%, O=59%, N=7% and H=2%) having a film thicknessof 100 nm is formed.

Subsequently, semiconductor layers 602 to 605 are formed on the basefilm 601. The semiconductor layers 602 to 605 are formed from asemiconductor film having an amorphous structure by a known method (asputtering method, an LPCVD method, or a plasma CVD method), and issubjected to a known crystallization process (a laser crystallizationmethod, a thermal crystallization method, or a thermal crystallizationmethod using a catalyst such as nickel). The crystalline semiconductorfilm thus obtained is patterned into desired shapes to obtain thesemiconductor layers. The semiconductor layers 602 to 605 are formedinto the thickness of from 25 to 80 nm (preferably 30 to 60 nm). Thematerial of the crystalline semiconductor film is not particularlylimited, but it is preferable to form the film using silicon, a silicongermanium (Si_(1-x)Ge_(x) (x=0.01 to 0.02)) alloy, or the like.

In this example, 55 nm thick amorphous silicon film is formed by plasmaCVD, and then, nickel-containing solution is held on the amorphoussilicon film. A dehydrogenating process of the amorphous silicon film isperformed (500° C. for one hour), and thereafter a thermalcrystallization process is performed (550° C. for four hours) thereto.Further, to improve the crystallinity thereof, laser anneal treatment isperformed to form the crystalline silicon film. Then, this crystallinesilicon film is subjected to a patterning process using aphotolithography method, to obtain the semiconductor layers 602 to 605.

Further, before or after the formation of the semiconductor layers 602to 605, a minute amount of impurity element (boron or phosphorus) may bedoped to control a threshold value of the TFT.

Besides, in the case where the crystalline semiconductor film ismanufactured by the laser crystal method, a pulse oscillation type orcontinuous-wave type gas state laser or solid state laser. As the gassate laser, excimer laser, Ar laser, or Kr laser may be used. As thesolid state laser, YAG laser, YVO₄ laser, YLF laser, YalO₃ laser, glasslaser, ruby laser, Ti: sapphire laser may be used.

In the case where those lasers are used, it is appropriate to use amethod in which laser light radiated from a laser oscillator iscondensed by an optical system into a linear beam, and is irradiated tothe semiconductor film. Although the conditions of the crystallizationshould be properly selected by an operator, in the case where theexciter laser is used, a pulse oscillation frequency is set as 300 Hz,and a laser energy density is as 100 to 400 mJ/cm² (typically 200 to 300mJ/cm²). In the case where the YAG laser is used, it is appropriate thatthe second harmonic is used to set a pulse oscillation frequency as 30to 300 kHz, and a laser energy density is set as 300 to 600 mJ/cm²(typically, 350 to 500 mJ/cm²). Then, laser light condensed into alinear shape with a width of 100 to 1000 μm, for example, 400 μm isirradiated to the whole surface of the substrate, and an overlappingratio (overlap ratio) of the linear laser light at this time may be setas 50 to 90%.

A gate insulating film 607 is then formed for covering the semiconductorlayers 602 to 605. The gate insulating film 607 is formed from aninsulating film containing silicon by plasma CVD or sputtering into afilm thickness of from 40 to 150 nm. In the example, the gate insulatingfilm 306 is formed from a silicon oxynitride film into a thickness of110 nm by plasma CVD (composition ratio Si=32%, O=59%, N=7%, and H=2%).Of course, the gate insulating film 607 is not limited to the siliconoxynitride film, an insulating film containing other silicon may beformed into a single layer of a lamination structure.

Beside, when the silicon oxide film is used, it can be formed by plasmaCVD in which TEOS (tetraethyl orthosilicate) and O₂ are mixed, with areaction pressure of 40 Pa, a substrate temperature of from 300 to 400°C., and discharged at a high frequency (13.56 MHZ) power density of 0.5to 0.8 W/cm². Good characteristics as the gate insulating film can beobtained in the silicon oxide film thus manufactured by subsequentthermal annealing at 400 to 500° C.

Then, as shown in FIG. 5A, on the gate insulating film 607, a firstconductive film 608 and a second conductive film 609 are formed intolamination to have a film thickness of 20 to 100 nm and 100 to 400 nm,respectively. In this example, the first conductive film 608 made from aTaN film with a film thickness of 30 nm and the second conductive film609 made from a W film with a film thickness of 370 nm are formed intolamination. The TaN film is formed by sputtering with a Ta target underan atmosphere containing nitrogen. Besides, the W film is formed by thesputtering method with a W target. The W film may be formed by thermalCVD using tungsten hexafluoride (WF₆).

Whichever method is used, it is necessary to make the material have lowresistance for use as the gate electrode, and it is preferred that theresistivity of the W film is set to less than or equal to 20 μΩcm. Bymaking the crystal grains large, it is possible to make the W film havelower resistivity. However, in the case where many impurity elementssuch as oxygen are contained within the W film, crystallization isinhibited and the resistance becomes higher. Therefore, in this example,by forming the W film having high purity by sputtering using a targethaving a purity of 99.9999%, and in addition, by taking sufficientconsideration to prevent impurities within the gas phase from mixingtherein during the film formation, a resistivity of from 9 to 20 μΩcmcan be realized.

Note that, in this example, the first conductive film 608 is made ofTaN, and the second conductive film 609 is made of W, but the materialis not particularly limited thereto, and either film may be formed of anelement selected from Ta, W, Ti, Mo, Al, Cu, Cr and Nd or an alloymaterial or a compound material containing the above element as its mainingredient. Besides, a semiconductor film typified by a polycrystallinesilicon film doped with an impurity element such as phosphorus may beused. Also, an alloy containing Ag, Pd, Cu can be used.

Besides, any combination may be employed such as a combination in whichthe first conductive film 608 is formed of tantalum (Ta) and the secondconductive film 609 is formed of W, a combination in which the firstconductive film 608 is formed of titanium nitride (TiN) and the secondconductive film 609 is formed of W, a combination in which the firstconductive film 608 is formed of tantalum nitride (TaN) and the secondconductive film 609 is formed of Al, or a combination in which the firstconductive film 608 is formed of tantalum nitride (TaN) and the secondconductive film 609 is formed of Cu, or a combination in which the firstconductive film 608 is formed of W, Mo, or the combination of W and Moand the second conductive film 609 is formed of Al and Si or Al and Tior Al and Sc or Al and Nd, further, the third conductive film (notshown) is formed from Ti, TiN or the combination of Ti and TiN.

Next, masks 610 to 613 made of resist are formed using aphotolithography method, and a first etching process is performed inorder to form electrodes and wirings as shown in FIG. 5B. This firstetching process is performed with the first and second etchingconditions. In This example, as the first etching conditions, an ICP(inductively coupled plasma) etching method is used, a gas mixture ofCF₄, Cl₂ and O₂ is used as an etching gas, the gas flow rate is set to25/25/10 sccm, and plasma is generated by applying a 500 W RF (13.56MHZ) power to a coil shape electrode under 1 Pa. A dry etching devicewith ICP (Model E645-ICP) produced by Matsushita Electric Industrial Co.Ltd. is used here. A 150 W RF (13.56 MHZ) power is also applied to thesubstrate side (test piece stage) to effectively apply a negativeself-bias voltage.

The W film is etched with the first etching conditions, and the endportion of the second conductive layer is formed into a tapered shape.In the first etching conditions, the etching rate for W is 200.39nm/min, the etching rate for TaN is 80.32 nm/min, and the selectivity ofW to TaN is about 2.5. Further, the taper angle of W is about 26° withthe first etching conditions.

Thereafter, as shown in FIG. 5B, the first etching conditions arechanged into the second etching conditions without removing the masks610 to 613 made of resist, a mixed gas of CF₄ and Cl₂ is used as anetching gas, the gas flow rate is set to 30/30 sccm, and plasma isgenerated by applying a 500 W RF (13.56 MHZ) power to a coil shapeelectrode under 1 Pa to thereby perform etching for about 15 seconds. A20 W RF (13.56 MHZ) power is also applied to the substrate side (testpiece stage) to effectively a negative self-bias voltage. The W film andthe TaN film are both etched on the same order with the second etchingconditions in which CF₄ and Cl₂ are mixed.

In the second etching conditions, the etching rate for W is 58.97nm/min, and the etching rate for TaN is 66.43 nm/min. Note that, theetching time may be increased by approximately 10 to 20% in order toperform etching without any residue on the gate insulating film.

In the first etching process, the end portions of the first and secondconductive layers are formed to have a tapered shape due to the effectof the bias voltage applied to the substrate side by adopting masks ofresist with a suitable shape. The angle of the tapered portions may beset to 15° to 45°. Thus, first shape conductive layers 615 to 618 (firstconductive layers 615 a to 618 a and second conductive layers 615 b to618 b) constituted of the first conductive layers and the secondconductive layers are formed by the first etching process. Referencenumeral 620 denotes a gate insulating film, and regions of the gateinsulating film which are not covered by the first shape conductivelayers 615 to 618 are made thinner by approximately 20 to 50 nm byetching.

Then, a first doping process is performed to add an impurity element forimparting an n-type conductivity to the semiconductor layer withoutremoving the mask made of resist (FIG. 15B). Doping may be carried outby an ion doping method or an ion injecting method. The condition of theion doping method is that a dosage is 1×10¹³ to 5×10¹⁵ atoms/cm², and anacceleration voltage is 60 to 100 keV. In this example, the dosage is1.5×10¹⁵ atoms/cm² and the acceleration voltage is 80 keV.

As the impurity element for imparting the n-type conductivity, anelement which belongs to group 15 of the periodic table, typicallyphosphorus (P) or arsenic (As) is used, and phosphorus is used here. Inthis case, the conductive layers 615 to 618 become masks to the impurityelement for imparting the n-type conductivity, and high concentrationimpurity regions 621 to 624 are formed in a self-aligning manner. Theimpurity element for imparting the n-type conductivity is added to thehigh concentration impurity regions 621 to 624 in the concentrationrange of 1×10²⁰ to 1×10²¹ atoms/cm³.

Thereafter, the second etching process is performed without removing themasks made of resist as shown in FIG. 15C. The second etching process isperformed by third or fourth etching condition. Here, a mixed gas ofCF₄, Cl₂ is used as an etching gas, the gas flow rate is set to 30/30sccm, and plasma is generated by applying a 500 W RF (13.56 MHZ) powerto a coil shape electrode under 1 Pa to thereby perform etching forabout 60 seconds. A 20 W RF (13.56 MHZ) power is also applied to thesubstrate side (test piece stage) to effectively apply a negativeself-bias voltage. The W film and the TaN film are both etched on thesame order with the third etching conditions in which CF₄ and Cl₂ aremixed.

In the second etching process, the etching rate for W is 58.97 nm/min,the etching rate for TaN is 66.43. Note that, the etching time may beincreased by approximately 10 to 20% in order to perform etching withoutany residue on the gate insulating film.

Thereafter, as shown in FIG. 5C, the third etching conditions arechanged into the fourth etching conditions. Without removing the masks610-613 made of resist, a mixed gas of CF₄, Cl₂ and O₂ is used as anetching gas, the gas flow rate is set to 20/20/20 sccm, and plasma isgenerated by applying a 500 W RF (13.56 MHZ) power to a coil shapeelectrode under 1 Pa to thereby perform etching for about 20 seconds. A20 W RF (13.56 MHZ) power is also applied to the substrate side (testpiece stage) to effectively apply a negative self-bias voltage.

In the fourth etching conditions, etching rate for TaN is 14.83 nm/min.Therefore, the W film etched selectively. According to the fourthetching process, the second conductive layer 626-629 (first conductivelayer 626 a-629 a and second conductive layer 626 b-629 b) are formed.

Next, a second doping process is performed as shown in FIG. 6A. Firstconductive layers 626 a to 629 a and second conductive layers 626 b to629 b are used as masks to an impurity element, and doping is performedsuch that the impurity element is added to the semiconductor layer belowthe tapered portions of the first conductive layers. In this example,phosphorus (P) is used as the impurity element, and plasma doping isperformed with the dosage of 1.5×10¹⁴ atoms/cm², current density of 0.5A and the acceleration voltage of 90 keV.

Thus, low concentration impurity regions 631 a to 634 a, which overlapwith the first conductive layers and low concentration impurity regions631 b to 634 b, which do not overlap with the first conductive layersare formed in a self-aligning manner. The concentration of phosphorus(P) in the low concentration impurity regions 631 to 634 is 1×10¹⁷ to5×10¹⁸ atoms/cm³. Further, the impurity element is added to the highconcentration impurity regions 621-624 and the high concentrationimpurity regions 635-638 are formed.

New masks 639 and 640 are formed from resist, and a third doping processis performed. Impurity regions 641 to 642, to which an impurity elementis added that imparts the opposite conductivity type (p-type) from thesingle conductivity type (n-type) are formed to the semiconductorlayers, which become active layers of p-channel TFTs, by the thirddoping process. (See FIG. 6B.) The first conductive layers 627 a and thesecond conductive layer 627 b are used as masks against the impurityelement, the impurity element imparting p-type conductivity is added,and the impurity regions are formed in a self-aligning manner.

The impurity regions 641 to 642 are formed in Example 2 by ion dopingusing diborane (B₂H₆). Phosphorous is added to the impurity regions 641to 642 in differing concentrations, respectively, by the first dopingprocess and by the second doping process. However, doping is performedsuch that the concentration of the impurity element which imparts p-typeconductivity to each of the regions becomes from 2×10²⁰ to 2×10²¹atoms/cm³, and therefore no problems will develop with the regionsfunctioning as source regions and drain regions of p-channel TFTs.

The resist masks 639 and 640 are removed next, and a first interlayerinsulating film 643 is formed. In this example, as the first inter layerinsulating film 643, the lamination film is formed from the firstinsulating film 643 a containing silicon and nitride and the secondinsulating film 643 b containing silicon and oxygen.

An insulting film containing silicon is formed having a thickness of 100to 200 nm, using plasma CVD or sputtering, as the first interlayerinsulating film 643 a. A silicon oxynitride film is formed with a filmthickness of 100 nm by plasma CVD in Example 2. The first interlayerinsulating film 643 a is of course not limited to the silicon oxynitridefilm, and other insulating films containing silicon may be used in asingle layer or a lamination structure.

Next, a process for activating the impurity elements added to each ofthe semiconductor layers is performed. Thermal annealing using anannealing furnace is performed for the activation process. Thermalannealing may be performed in a nitrogen atmosphere having an oxygenconcentration of 1 ppm or less, preferably 0.1 ppm or less, at 400 to700° C., typically between 500 and 550° C. The activation process isperformed in Example 2 by heat treatment at 550° C. for four hours. Notethat, in addition to thermal annealing, laser annealing and rapidthermal annealing (RTA) can also be applied.

Note also that, in Example 2, nickel used as a catalyst duringcrystallization is gettered into the impurity regions 635, 636, 637, and638 containing phosphorous at a high concentration at the same time asthe above activation process is performed. The nickel concentrationwithin the semiconductor layers that mainly become channel formingregions is thus reduced. The value of the off current is reduced forTFTs having channel forming regions thus formed, and a high electricfield effect mobility is obtained because of the good crystallinity.Thus, good properties can be achieved.

Further, the activation process may also be performed before forming thefirst interlayer insulating film. However, when using a wiring materialwhich is weak with respect to heat, it is preferable to perform theactivation process after forming the interlayer insulating film(insulating film containing silicon as its main constituent, siliconnitride film, for example) in order to protect the wirings and the like,as in Example 2.

The doping process may be performed, and the first interlayer insulatingfilm may be formed after performing the activation process.

In addition, heat treatment is performed for 1 to 12 hours at 300 to550° C. in an atmosphere containing hydrogen of 3 to 100%, performinghydrogenation of the semiconductor layers. Heat treatment is performedfor one hour at 410° C. in a atmosphere containing approximately 3%hydrogen in Example 2. This process is one for terminating danglingbonds of the semiconductor layers by hydrogen contained in theinterlayer insulating film. Plasma hydrogenation (using hydrogen excitedby plasma) may be performed as another means of hydrogenation.

Further, when using a laser annealing method as the activation process,it is preferable to irradiate laser light such as that from an excimerlaser or a YAG laser after performing the above hydrogenation process.

A second interlayer insulating film 643 b is formed next on the firstinterlayer insulating film 643 a from insulating film containing siliconwith a thickness of 1-2 μm by plasma CVD or sputtering. A silicon oxidefilm having a film thickness of 1.2 μm is formed in Example 2. Ofcourse, the second insulating film 643 b is not limited to the abovementioned film, an insulating film containing other silicon may beformed into a single layer or a lamination structure.

Then the first interlayer insulating film 643 made from first insulatingfilm 643 a and second insulating film 643 b can be formed.

Next, patterning is performed in order to form contact holes forreaching the impurity regions 635, 636, 637, and 638.

In addition, the first insulating film 643 a and the second insulatingfilm 643 b are insulating film contained silicon formed plasma CVD, sothat dry etching method or wet etching method can be used for forming acontact hole. However, in this embodiment, wet etching method is usedfor etching the first insulating film, and the dry etching method isused for etching the second insulating film.

First, the second insulating film 643 b is etched. Here, a mixedsolution (Stella chemifa Inc., brand name LAL 500) contained 7.14% ofhydrogen ammonium fluoride (NH₄HF₂) and 15.4% of ammonium fluoride(NH₄F) is used as a etchant to conduct a wet etching at 20° C.

Next, the first insulating film 643 a is etched. CHF₄ is used as anetching gas, and gas flow rates are set to 35 sccm. An 800 W RF electricpower is applied at a pressure of 1 Pa, and dry etching is performed.

Wirings 645 to 651 and cathode 652 are formed that connect electricallywith high concentration impurity regions 635, 636, 637, and 638respectively. In this embodiment, these wirings are formed by patterningAl film in 500 nm thicknesses. Besides, a single layer constituted Ti,TiN, Al:Si and the like, or a lamination layer laminated Ti, TiN, Al:Si,and Ti in turn can also be used.

In this embodiment, the cathode 652 is formed simultaneously with wiringformation, and to serve a function as a wiring of high concentrationimpurity region 638.

The insulating film is formed in 1 μm thickness. As material forming aninsulating film, a film containing silicon oxide is used in thisembodiment. Another films such as insulating film containing siliconnitride, or silicon oxide nitride, the organic resin film, polyimide,polyamide, acrylic (photosensitive acrylic is included), BCB(benzocyclobutene), or the like may also be used.

An opening portion is formed to correspond to the cathode 652 of thisinsulating film, and the insulating film 653 is formed (FIG. 7B).

Specifically, the insulating film 653 is formed by that the insulatingfilm is formed in 1 μm thick using a photosensitive acrylic, and afterthat it is patterned using photolithography method and is performedetching treatment.

On the exposed cathode 652 at the opening portion in the insulating film653, inorganic conductive layer 654 is formed by evaporation method. Inthis embodiment, as materials for forming the inorganic conductive layer654, a conductive nitride, a carbide, an oxide, a boride, and a silicidethat are composed of elements of second group of the periodic system canbe used. However, inorganic conductive layer 654 is formed by usingnitride calcium (CaN).

In this embodiment, the inorganic conductive layer 654 is formed byusing a vacuum evaporation method maintaining a thickness of from 1 to50 nm (preferably, from 10 to 20 nm). In this embodiment, the inorganicconductive layer 654 is formed maintaining a thickness of 30 nm.

As shown in FIG. 8, an organic compound layer 655 is formed on theinorganic conductive layer 654 by an evaporation method. In thisembodiment, the state of forming one kind of organic compound layer fromorganic compound layers that are constituted organic compounds emittingthree kinds of luminescence, red, green, and blue is illustrated. Thecombination of the organic compounds that form three kinds of organiccompounds layer is described with reference to FIG. 9.

A light emitting element shown in FIG. 9A is constituted a cathode 901,an inorganic conductive layer 902, an organic compound layer 903, abarrier layer 908, and an anode 909. The organic compound layer 903 hasa lamination structure constituted an electron transporting layer 904, ablocking layer 905, a light emitting layer 906, and a positive holetransporting layer 907. As for the material that constitute redluminescent light emitting element and the thickness are illustrated inFIG. 9B, as for the material that constitute green luminescent lightemitting element and the thickness are illustrated in FIG. 9C, and asfor the material that constitute blue luminescent light emitting elementand the thickness are illustrated in FIG. 9D respectively.

First, an organic compound layer emitting red light is formed.Specifically, a tris (8-quinolinolato) aluminum (hereinafter referred toas the Alq₃) as an electron transporting organic compound is formed intoan electron transporting layer 904 in a 40 nm film thickness. Abasocuproin (hereinafter referred to as the BCP) as a blocking organiccompound is formed into a blocking layer 905 in a 10 nm film thickness.A 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphyrin-platinum (hereinafterreferred to as the PtOEP) as a luminescent organic compound isco-deposited to form the light emitting layer 906 with organic compounds(hereinafter referred to as the host materials) a4,4′-dicarbazol-biphenyl (hereinafter referred to as the CBP) to serveas the host in a 30 nm film thickness. A4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as the α-NPD) as a positive hole transporting organic compound isformed into a hole transporting layer 907 in a 40 nm film thickness.Thereby, a red luminescent organic compound layer can be formed.

Although the case of forming a red luminescent organic compound layerusing 5 kinds of organic compounds with different functions is explainedhere, the present invention is not limited thereto, and known materialscan be used as the organic compound showing the red luminescence.

A green luminescent organic compound layer is formed. Specifically, anAlq₃ as an electron transporting organic compound is formed into theelectron transporting layer 904 in a 40 nm film thickness. A BCP as ablocking organic compound is formed into the blocking layer 905 in a 10nm film thickness. The light emitting layer 906 is formed by that a CBPused as a positive hole transmitting host material is co-deposited witha tris (2-phenyl pyridine) iridium (Ir(ppy)₃) in a 30 nm film thickness.An α-NPD as a positive hole transporting organic compound is formed intothe positive hole transporting layer 907 in a 40 nm film thickness.Thereby, a green luminescent organic compound layer can be formed.

Although the case of forming a green luminescent organic compound layerusing 4 kinds of organic compounds with different functions is explainedhere, the present invention is not limited thereto, and known materialscan be used as the organic compound showing the green luminescence.

A blue luminescent organic compound layer is formed. Specifically, anAlq₃ as an electron transporting organic compound is formed into theelectron transporting layer 904 in a 40 nm film thickness. A BCP as ablocking organic compound is formed into the blocking layer 905 in a 10nm film thickness. An α-NPD as a luminescent organic compound and apositive hole transporting organic compound is formed into the lightemitting layer 906 in a 40 nm film thickness. Thereby, a blueluminescent organic compound layer can be formed.

Although the case of forming a blue luminescent organic compound layerusing 3 kinds of organic compounds with different functions is explainedhere, the present invention is not limited thereto, and known materialscan be used as the organic compound showing the blue light emission.

By forming the above-mentioned organic compounds on the cathode, anorganic compound layer emitting the red luminescence, the greenluminescence and the blue luminescence can be formed in the pixelportion.

In the light emitting structure in this embodiment, the anode 909 madeout of transparent conductive film is formed by sputtering after theorganic compound layer 903 is formed. According to this, the surface ofthe organic compound layer 903 is damaged when the anode 909 is formed.In this embodiment, a barrier layer 903 is provided on the organiccompound layer 903 in order to prevent the organic compound layer 903from being damaged.

As a material forming the barrier layer 908, materials with large workfunction such as gold and silver, and Cu-Pc having a positive injectioncan be used. In this embodiment, the barrier film 908 is formed byforming gold maintaining a thickness of 10 nm. (FIG. 9A)

Next, an anode 656 made from transparent conductive film is formedcovering an organic compound layer 655 and an insulating layer 653 asshown in FIG. 8B. In this embodiment, as a material of forming the anode656, an indium-tin oxide (ITO) film or a transparent conductive filmformed maintaining a thickness of 80 to 120 nm having 2 to 20[%] of azinc oxide (ZnO) added to an indium oxide is used. When a transparentconductive film have a large work function, another known materials canbe used to form the anode 656.

As shown in FIG. 8B, an element substrate having a light emittingelement 657 that is composed of the cathode 652 connected to the currentcontrol TFT 704 electrically, the insulating layer 653 formed betweenthe cathode 652 and the first electrode (not illustrated) included innext pixel, the inorganic conductive layer 654 formed on the cathode652, organic compound layer 655 formed on the inorganic conductive layer654, and the anode 656 formed on the organic compound layer 655 and theinsulating layer 653 can be formed.

Note that, in the process of manufacturing the light emitting device inthis embodiment, although the source signal lines are formed bymaterials which form the gate electrodes, and although the gate signallines are formed by wiring materials which forms the source and drainelectrodes, with relation to the circuit structure and process, othermaterials may also be used.

Further, a driver circuit 705 having an n-channel TFT 701 and ap-channel TFT 702, and a pixel portion 706 having a switching TFT 703and a current control TFT 704 can be formed on the same substrate.

The n-channel TFT 701 of the driver circuit 705 has the channel formingregion 501, the low concentration impurity region 631 (GOLD region)which overlaps with the first conductive layer 626 a forming a portionof the gate electrode, and the high concentration impurity region 635which functions as a source region or a drain region. The p-channel TFT702 has the channel forming region 502, and the impurity regions 641 and642 that function as source regions or drain regions.

The switching TFT 703 of the pixel portion 706 has the channel formingregion 503, the low concentration impurity region 633 a (LDD region)which overlap with the first conductive layer 628 a, the lowconcentration impurity region 633 b (LDD region) which does not overlapwith the first conductive layer 628 a, and the high concentrationimpurity region 637 which functions as a source region or a drainregion.

The current control TFT 704 of the pixel portion 706 has the channelforming region 504, the low concentration impurity region 634 a (LDDregion) which overlap with the first conductive layer 629 a, the lowconcentration impurity region 634 b (LDD region) which does not overlapwith the first conductive layer 628 a, and the high concentrationimpurity region 638 which function as source regions or drain regions.

In this embodiment, the driving voltage of a TFT is 1.2 to 10 V,preferably 2.5 to 5.5 V.

When the display of the pixel portion is active (case of the movingpicture display), a background is displayed by pixels in which the lightemitting elements emit light and a character is displayed by pixels inwhich the light emitting elements do not emit light. However, in thecase where the moving picture display of the pixel portion is still fora certain period or more (referred to as a standby time in the presentspecification), for the purpose of saving electric power, it isappropriate that a display method is changed (inverted). Specifically, acharacter is displayed by pixels in which EL elements emit light (alsocalled a character display), and a background is displayed by pixels inwhich light emitting elements do not emit light (also called abackground display).

A detailed top surface structure of a pixel portion is shown in FIG.10A, and a circuit diagram thereof is shown in FIG. 10B. FIGS. 10A and10B denoted by a same reference numerals.

In FIGS. 10A and 10B, a switching TFT 1000 provided on a substrate isformed by using the switching TFT (n-channel type) TFT 703 of FIG. 8.Therefore, an explanation of the switching (n-channel type) TFT 703 maybe referred for an explanation of the structure. Further, a wiringindicated by reference numeral 1002 is a gate wiring for electricallyconnecting with gate electrodes 1001 (1100 a and 1001 b) of theswitching TFT 1000.

Note that, in this embodiment, a double gate structure is adopted, inwhich two channel forming regions are formed, but a single gatestructure, in which one channel forming region is formed, or a triplegate structure, in which three channel forming regions are formed, mayalso be adopted.

Further, a source of the switching TFT 1000 is connected to a sourcewiring 1003, and a drain thereof is connected to a drain wiring 1004.The drain wiring 1004 is electrically connected with a gate electrode1006 of a current control TFT 1005. Note that the current control TFT1005 is formed by using the current control (n-channel type) TFT 704 ofFIG. 8. Therefore, an explanation of the current control (n-channeltype) TFT 704 may be referred for an explanation of the structure. Notethat, although the single gate structure is adopted in this embodiment,the double gate structure or the triple gate structure may also beadopted.

Further, a source of the current control TFT 1005 is electricallyconnected with a current supply line 1007, and a drain thereof iselectrically connected with a drain wiring 1008. Besides, the drainwiring 1008 is electrically connected with a cathode 1009 indicated by adotted line.

A wiring indicated by reference numeral 1010 is a gate wiring connectedwith the gate electrode 1012 of the erasing TFT 1011. Further, a sourceof the erasing TFT 1011 is electrically connected to the current supplyline 1007, and a drain thereof is electrically connected to the drainwiring 1004.

The erasing TFT 1011 is formed like a current controlling TFT (n-channeltype) 704 in FIG. 8. Therefore, an explanation of the structure isreferred to that of the current controlling TFT (n-channel type) 704. Inthis embodiment, a single gate structure is described though, a doublegate structure or a triple gate structure can be used.

At this time, a storage capacitor (condenser) is formed in a regionindicated by reference numeral 1013. The capacitor 1013 is formed by asemiconductor film 1014 electrically connected with the current supplyline 1007, an insulating film (not shown) of the same layer as a gateinsulating film, and the gate electrode 1006. Further, a capacitorformed by the gate electrode 1006, the same layer (not shown) as a firstinterlayer insulating film, and the current supply line 1007 may be usedas a storage capacitor.

The light emitting element 1015 shown in circuit diagram in FIG. 10B iscomposed of the cathode 1009, an organic compound layer (notillustrated) formed on the cathode 1009, and an anode (not illustrated)formed on the organic compound layer. In the present invention, thecathode 1009 is connected with a source region and a drain region of thecurrent controlling TFT 1005.

A counter potential is supplied to the anode of the light emittingelement 1005. In addition, the power source potential is supplied to thepower supply line 1007. A potential difference between the counterpotential and the power source potential is always maintained at such alevel that causes the light emitting element to emit light when thepower source potential is applied to the pixel electrode. The powersource potential and the counter potential are supplied to the lightemitting device of the present invention by means of a power sourceprovided by an externally-attached IC chip or the like. In the presentspecification, the power source supplying a counter potential isreferred to as the counter power source 1016.

Example 3

Referring to FIG. 11, the external appearance of an active matrix typeluminescent device of the present invention will be described in thepresent example.

FIG. 11A is a top view of the luminescent device, and FIG. 11B is asectional view taken on line A-A′ of FIG. 11A. Reference number 1101represents a source side driving circuit, which is shown by a dottedline; 1102, a pixel section; 1103, a gate side driving circuit; 1104, acover material; and 1105, a sealant. A space is surrounded by thesealant 1105.

Reference number 1108 represents an interconnection for transmittingsignals inputted to the source signal line driving circuit 1101 and thegate signal line driving circuit 1103. The interconnection 1108 receivesvideo signals or clock signals from a flexible print circuit (FPC) 1109,which will be an external input terminal. Only the FPC is illustrated,but a printed wiring board (PWB) may be attached to this FPC. Theluminescent device referred to in the present specification may be thebody of the luminescent device, or a product wherein an FPC or a PWB isattached to the body.

The following will describe a sectional structure, referring to FIG.11B. The driving circuits and the pixel section are formed on thesubstrate 1110, but the source side driving circuit 1101 as one of thedriving circuits and the pixel section 1102 are shown in FIG. 11B.

In the source side driving circuit 1101, a CMOS circuit wherein ann-channel type TFT 1113 and a p-channel type TFT 1114 are combined isformed. The TFTs constituting the driving circuit may be composed ofknown CMOS circuits, PMOS circuits or NMOS circuits. In the presentexample, a driver-integrated type, wherein the driving circuit is formedon the substrate, is illustrated, but the driver-integrated type may notnecessarily be adopted. The driver may be fitted not to the substratebut to the outside.

The pixel section 1102 is composed of plural pixels including acurrent-controlling TFT 1111 and an anode 1112 electrically connected tothe drain of the TFT 1111.

On the both sides of the anode 1112, insulators 1113 are formed, and anorganic compound layer 1114 is formed on the anode 1112. Furthermore,non-organic conductive layer 1116 is formed on the organic compoundlayer 1114 and a cathode 1117 is formed on the non-organic conductivelayer 1116. In this way, a luminescent element 1118 composed of theanode 1112, the organic compound layer 1114 and the cathode 1117 isformed.

The cathode 1117 also functions as an interconnection common to all ofthe pixels, and is electrically connected through the interconnection1108 to the FPC 1109.

In order to confine the luminescent element 1118 formed on the substrate1110 airtightly, the cover material 1104 is adhered with the sealant1105. A spacer made of a resin film may be set up to keep a giveninterval between the cover material 1104 and the luminescent element1018. An inert gas such as nitrogen is filled into the space 1107 insidethe sealant 1105. As the sealant 1105, an epoxy resin is preferablyused. The sealant 1105 is desirably made of a material through whichwater content or oxygen is transmitted as slightly as possible.Furthermore, it is allowable to incorporate a material having moistureabsorption effect or a material having antioxidation effect into thespace 1107.

In the present example, as the material making the cover material 1104,there may be used a glass substrate, a quartz substrate, or a plasticsubstrate made of fiber glass-reinforced plastic (FRP), polyvinylfluoride (PVF), mylar, polyester or polyacrylic resin.

After the adhesion of the cover material 1104 to the substrate 1110 withthe sealant 1105, a sealant is applied so as to cover the side faces(exposure faces).

As described above, the luminescent element is airtightly put into thespace 1107, so that the luminescent element can be completely shut outfrom the outside and materials promoting deterioration of the organiccompound layer, such as water content and oxygen, can be prevented frominvading this layer from the outside. Consequently, the luminescentdevice can be made highly reliable.

The structure of the present example may be freely combined with thestructure of example 1 or 2.

Example 4

Example 1 to 3 describes an active matrix type luminescent device havinga top gate transistor. However, the transistor structure of the presentinvention is not limited thereto and bottom gate transistors (typicallyreverse stagger transistors) may also be used in carrying out thepresent invention as shown in FIG. 12. The reverse stagger transistorsmay be formed by any method.

FIG. 12A is a top view of a light emitting device that uses bottom gatetransistors. Note that the sealing in not conducted yet by sealingsubstrate. A source side driving circuit 1201, a gate side drivingcircuit 1202, and a pixel portion 1203 are formed therein. FIG. 12Bshows in section a region a 1204 of the pixel portion 1203. Thesectional view is obtained by cutting the light emitting device alongthe line x-x′ in FIG. 12A.

FIG. 12B illustrates only a current controlling transistor out oftransistors that constituted in a pixel portion 1203. Reference symbol1211 denotes a substrate and 1212 denotes an insulating film to serve asa base (hereinafter referred to as a base film). A transparent substrateis used for the substrate 11211, typically, a glass substrate, a quartzsubstrate, a glass ceramic substrate, or a crystallized glass substrate.However, the one that can withstand the highest process temperatureduring the manufacture process has to be chosen.

The base film 1212 is effective especially when a substrate containing amovable ion or a conductive substrate is used. If a quartz substrate isused, the base film may be omitted. An insulating film containingsilicon is used for the base film 1212. The term insulating filmcontaining silicon herein refers to an insulating film containing oxygenor nitrogen in a given ratio to the content of silicon, specifically, asilicon oxide film, a silicon nitride film, or a silicon oxynitride film(SiOxNy: x and y are arbitrary integers).

Reference symbol 1213 denotes a current controlling transistor that is ap-channel transistor. Note that, in this example, cathode 1223 ofluminescent element 1229 is connected the current control transistor1213. Therefore, the cathode 1223 are preferably made from p-channel TFTbut also made from n-channel TFT.

The current controlling transistor 1213 is composed of an active layerwhich comprising source region 1214, drain region 1215 and channelforming region 1216, a gate insulating film 1217, a gate electrode 1218,a interlayer insulating film 1219, a source wiring line 1220, and adrain wiring line 1221. The current controlling transistor 1213 in thisexample is a p-channel transistor.

The switching transistor has a drain region connected to the gateelectrode 1218 of the current controlling transistor 1213. The gateelectrode 1218 of the current controlling transistor 1213 iselectrically connected to the drain region (not shown) of the switchingtransistor through a drain wiring line (not shown), to be exact. Thegate electrode 1218 has a single gate structure but may take amulti-gate structure. The source wiring line 1220 of the currentcontrolling transistor 1213 is connected to a current supplying line(not shown).

The current controlling transistor 1213 is an element for controllingthe amount of current supplied to the EL element, and a relatively largeamount of current flows through this transistor. Therefore, it ispreferable to design the current controlling transistor to have achannel width (W) wider than the channel width of the switchingtransistor. It is also preferable to design the current controllingtransistor to have a rather long channel length (L) in order to avoidexcessive current flow in the current controlling transistor 1213.Desirably, the length is set such that the current is 0.5 to 2 μA(preferably 1 to 1.5 μA) per pixel.

If the active layer (channel formation region, in particular) of thecurrent controlling transistor 1213 is formed thick (desirably 50 to 100nm, more desirably 60 to 80 nm), degradation of the transistor can beslowed.

After the current controlling transistor 1213 is formed, the interlayerinsulating film 1219 is formed and cathode 1223 that is electricallyconnected to the current controlling transistor 1213 is formed. In thisexample, the current controlling transistor 1213, the wiring thatconnects the cathode 1223 electrically and cathode 1223 are formed atthe same time and same material. As the materials of cathode 1223, theconductive film having small working function is preferably used. Inthis example, the cathode 1223 formed from Al.

After the cathode 1223 is formed, an insulating film 1224 is formed. Theinsulating film 1224 serves as a so-called bank.

A non-organic conductive layer 1225 is formed next. Note that in thisexample, the luminescent element has the same structure as the onedescribed in example 1. Barrier layer 1227 is formed on the organiccompound layer 1226 and the organic compound layer 1226 is formed on thenon-organic conductive layer 1225. Note that, as the materials ofnon-organic conductive layer 1225, organic compound layer 1226 andbarrier layer 1227, the materials described in example 1 can be used.

Next, an anode 1228 is formed on the barrier layer 1227. As thematerials of anode 1228, a transparent conductive film is used. Notethat, in this example, anode 1228 is formed from ITO for 110 nmthickness.

Then, A light emitting device having a reverse stagger transistorstructure complete. The light emitting device manufactured in accordancewith this example emits light in the direction indicated by the arrow inFIG. 12B (toward the top face).

A reverse stagger transistor can be fabricated with a smaller number ofmanufacture steps than needed to fabricate a top gate transistor.Therefore it is very advantageous for cost down, which is one of theobjects of the present invention.

This example describes the light emitting device having the elementstructure that having a reverse stagger type TFT and light is emittedfrom cathode side of luminescent element. But the reverse stagger typeTFT of this example also combined with the various luminescent elementsshowed in example 1. Further, this example may be combined freely withany of the manufacturing method or materials of Examples 2 and sealingstructure of Example 3.

Example 5

In the present example, a case in which a passive type (simple matrixtype) luminous device having an element structure of the presentinvention is produced will be described, referring to FIG. 13. In FIG.13, reference numbers 1301 and 1302 represent a glass substrate and ananode made of a transparent conductive film, respectively. In thepresent example, a compound of indium oxide and zinc oxide is formed forthe transparent conductive film by vapor deposition. A plurality of theanodes 1302, which are not illustrated in FIG. 13, are arranged in theform of stripe parallel to the paper face.

Banks 1303 made of an insulating material are formed to cross the anode1302 arranged in the stripe form. The banks 1303 are formedperpendicularly to the paper face to contact the anodes 1302.

Next, an organic compound layer 1304 is formed. As the material whichmakes the organic compound layer 1304, a known material which can giveluminescence, as well as the materials described in Examples 1 and 2,can be used.

For example, by forming an organic compound layer giving redluminescence, an organic compound layer giving green luminescence, andan organic compound layer giving blue luminescence, a luminous devicegiving three types of luminescence rays can be formed. Since the organiccompound layer 1304 composed of these layers is formed along groovesmade in the banks 1303, the layer 1304 is arranged in the stripe formperpendicular to the paper face.

In the structure of the luminous element in the present example, aninorganic conductive layer 1306 is formed by vacuum vapor depositionafter the formation of the organic compound layer 1304.

Next, a cathode 1307 is formed. The cathode 1307 is formed on theinorganic conductive layer 1306 by vapor deposition using a metal mask.

Since the lower electrodes (the anodes 1302) are transparent anodes inthe present example, light generated in the organic compound layer isradiated downward (from the substrate 1301).

Next, a ceramic substrate is prepared as a sealing substrate 1309. Sincethe sealing substrate 1309 may have light-shading property in thestructure of the present example, the ceramic substrate is used.However, a substrate made of plastic or glass may be used.

The thus-prepared sealing substrate 1309 is adhered to the substrate1301 with a sealant 1310 made of an ultraviolet hardening resin. Theinside 1308 of the sealant 1310 is an airtightly-closed space, and theinside is filled with an inert gas such as nitrogen or argon. It iseffective to put a moisture absorbent, a typical example of which isbarium oxide, in the airtightly closed space 1308. At last, a flexibleprinted circuit (FPC) 1311 is fitted to the anodes to complete a passivetype luminous device. The present example may be carried out in thestate that the materials described in Examples 1 and 2 may be freelycombined in the present example to form the organic compound layer, orthe sealing structure described in Example 3 is applied to the presentexample.

Example 6

Being self-luminous, a light emitting device using a light emittingelement has better visibility in bright places and wider viewing anglethan liquid crystal display devices. Therefore various electricappliances can be completed by using the light emitting device of thepresent invention.

Given as examples of an electric appliance that employs a light emittingdevice manufactured in accordance with the present invention are videocameras, digital cameras, goggle type displays (head mounted displays),navigation systems, audio reproducing devices (such as car audio andaudio components), notebook computers, game machines, portableinformation terminals (such as mobile computers, cellular phones,portable game machines, and electronic books), and image reproducingdevices equipped with recording media (specifically, devices with adisplay device that can reproduce data in a recording medium such as adigital video disk (DVD) to display an image of the data). Wide viewingangle is important particularly for portable information terminalsbecause their screens are often slanted when they are looked at.Therefore it is preferable for portable information terminals to employthe light emitting device using the light emitting element. Specificexamples of these electric appliance are shown in FIGS. 14A to 14H.

FIG. 14A shows a display device, which is composed of a case 2001, asupport base 2002, a display unit 2003, speaker units 2004, a videoinput terminal 2005, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2003. Since the light emitting device having the light emitting elementis self-luminous, the device does not need back light and can make athinner display unit than liquid crystal display devices. The displaydevice refers to all display devices for displaying information,including ones for personal computers, for TV broadcasting reception,and for advertisement.

FIG. 14B shows a digital still camera, which is composed of a main body2101, a display unit 2102, an image receiving unit 2103, operation keys2104, an external connection port 2105, a shutter 2106, etc. The lightemitting device manufactured in accordance with the present inventioncan be applied to the display unit 2102.

FIG. 14C shows a notebook personal computer, which is composed of a mainbody 2201, a case 2202, a display unit 2203, a keyboard 2204, anexternal connection port 2205, a pointing mouse 2206, etc. The lightemitting device manufactured in accordance with the present inventioncan be applied to the display unit 2203.

FIG. 14D shows a mobile computer, which is composed of a main body 2301,a display unit 2302, a switch 2303, operation keys 2304, an infraredport 2305, etc. The light emitting device manufactured in accordancewith the present invention can be applied to the display unit 2302.

FIG. 14E shows a portable image reproducing device equipped with arecording medium (a DVD player, to be specific). The device is composedof a main body 2401, a case 2402, a display unit A 2403, a display unitB 2404, a recording medium (DVD or the like) reading unit 2405,operation keys 2406, speaker units 2407, etc. The display unit A 2403mainly displays image information whereas the display unit B 2404 mainlydisplays text information. The light emitting device manufactured inaccordance with the present invention can be applied to the displayunits A 2403 and B 2404. The image reproducing device equipped with arecording medium also includes home-video game machines.

FIG. 14F shows a goggle type display (head mounted display), which iscomposed of a main body 2501, display units 2502, and arm units 2503.The light emitting device manufactured in accordance with the presentinvention can be applied to the display units 2502.

FIG. 14G shows a video camera, which is composed of a main body 2601, adisplay unit 2602, a case 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, eye pieceportion 2610 etc. The light emitting device manufactured in accordancewith the present invention can be applied to the display unit 2602.

FIG. 14H shows a cellular phone, which is composed of a main body 2701,a case 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2703. If the display unit 2703 displays white letters on blackbackground, the cellular phone consumes less power.

If the luminance of light emitted from organic materials is raised infuture, the light emitting device can be used in front or rearprojectors by enlarging outputted light that contains image informationthrough a lens or the like and projecting the light.

These electric appliances now display with increasing frequencyinformation sent through electronic communication lines such as theInternet and CATV (cable television), especially, animation information.Since organic materials have very fast response speed, the lightemitting device is suitable for animation display.

In the light emitting device, light emitting portions consume power andtherefore it is preferable to display information in a manner thatrequires less light emitting portions. When using the light emittingdevice in display units of portable information terminals, particularlycellular phones and audio reproducing devices that mainly display textinformation, it is preferable to drive the device such that non-lightemitting portions form a background and light emitting portions formtext information.

As described above, the application range of the light emitting devicemanufactured by using the deposition device of the present invention isso wide that it is applicable to electric appliances of any field. Theelectric appliances of this embodiment can employ as their display unitsany light emitting device shown in Embodiments 1 to 5, which is formedby the deposition method shown in Embodiments 1 to 3.

Example 7

In the present example, results obtained by measuring elementcharacteristics of the following structures will be described: (1) aconventional luminous element structure in which an alloy containing analkali metal, which has a small work function, is used for its cathode;(2) a conventional luminous structure wherein a conventional cathodebuffer layer (insulating material) is set between its cathode and itsorganic compound layer; and (3) a structure of the present inventionwherein an inorganic conductive layer is used as a part of a luminouselement to form the element.

About the element characteristic of the luminous element structure (1)wherein an alloy containing an alkali metal, which has a small workfunction, was used for its cathode, an alloy of aluminum and lithium(Al:Li alloy) was used for the cathode of the luminous element toproduce the luminous element. The current characteristic and the voltagecharacteristic in this case are shown in FIGS. 15A and 15B,respectively. The structure of the produced element was as follows:Al:Li (100 nm) (cathode)/Alq₃ (50 nm)/α-NPD (30 nm)/Cu-Pc (20 nm)/ITO(anode).

As the current characteristic, a luminance of 1000 cd/m² was obtained at20 mA/cm². As the voltage characteristic, a luminance of 1000 cd/m² wasobtained at 7 V.

About the electric characteristics of the luminous element structure (2)wherein a conventional cathode buffer layer (insulating material) wasset between its cathode and its organic compound layer, a cathode bufferlayer (LiF) was set between the cathode and the organic compound layerof the luminous element, to produce the element. The currentcharacteristic and the voltage characteristics in this case are shown inFIGS. 16A and 16B, respectively. The structure of the produced elementwas as follows: Al(100 nm) (cathode)/LiF (1 nm)(cathode buffer)/Alq₃ (50nm)/α-NPD (30 nm)/Cu-Pc (20 nm)/ITO (anode).

The current characteristic was substantially the same as in the caseusing the Al:Li alloy as the cathode, and a brightness of 1000 cd/m² wasobtained at 25 mA/cm². As the voltage characteristics, a luminance of1000 cd/m was obtained at 7 V in the same manner.

About the element characteristic of the structure (3) wherein aninorganic conductive layer was used as a part of a luminous element toform the element, a conductive film made of each of inorganic compounds(Ca₃N₂, Mg₂N₃ and MgB₂) was formed between the cathode and the organiccompound layer of the luminous element. The current characteristic andthe voltage characteristic of these luminous elements having thestructure of the present invention are shown in FIGS. 17 to 19. Thestructure of the produced luminous element is as follows: Al(100 nm)(cathode)/conductive film (Ca₃N₂, Mg₂N₃ or MgB₂) (100 nm)/Alq₃ (50nm)/α-NPD (30 nm)/Cu-Pc (20 nm)/ITO (anode).

In the luminous elements using the inorganic conductive film having theabove-mentioned structure as their one part, a luminance of 1000 cd/m²can be obtained at 25 mA/cm² even if any one of the inorganic materialsis used. As the voltage characteristic thereof, a luminance of 1000cd/m² was obtained at 6.5 V. This is the same as in the conventionalluminous elements ((1) the conventional luminous element structure inwhich the alloy containing an alkali metal, which has a small workfunction, was used for its cathode; and (2) the conventional luminousstructure wherein the conventional cathode buffer layer (insulatingmaterial) was set between its cathode and its organic compound layer),and demonstrates that the inorganic conductive layer of the presentinvention produces no bad effect on element characteristics whencompared with the conventional element structures.

About the three materials of calcium nitride, magnesium nitride andmagnesium boride, the resistivity and the work function thereof weremeasured. The resistivity was obtained by forming aluminum electrodes atintervals of 1.9 cm, forming a film made of each of the above-mentionedthree materials (film thickness: 70 nm, 30 nm and 40 nm in the case ofCa₃N₂, Mg₃N₂ and MgB₂, respectively) between the electrodes to have athickness of 3 cm, and then measuring the resistance value thereof witha tester.

The work function was measured using a contact voltage measuring method(measuring device: Fermi level measuring device FAC-1 (made by RikenKeiki Co., Ltd.)). The results are shown in Table 1. TABLE 1 ρ[10⁻⁶ Ωcm]Φ[eV] Ca₃N₂ 7.7 Less than 3.1 Mg₃N₂ 230 3.7 MgB₂ 150 3.8

The inorganic conductive layer in the present invention is a conductivefilm made of an inorganic compound containing an element belonging tothe II group in the periodic table, such as a nitride, a sulfide, or aboride. In the present invention, therefore, the diffusion of an alkalimetal, which is said to produce a bad effect on the properties of a TFT,can be still more prevented than in cases in which an alloy containingan alkali metal, which has a small work function, is used as a cathodematerial. Furthermore, in the present invention, the conductive layer ismade of a material having electric conductivity. Therefore, the presentinvention can overcome a problem that the layer becomes thinner when acathode buffer layer made of a conventional insulating material is used,without producing any effect on element characteristics. In other words,by using an inorganic conductive layer in a luminous element in thepresent invention, the above-mentioned advantageous effects can beobtained while the same properties as in the case using conventionalcathode material and a conventional cathode buffer layer are maintained.

In the present invention, an inorganic conductive layer made of aninorganic compound having a small work function and electricconductivity is formed between a cathode and an organic compound layer,whereby it becomes unnecessary to make the film extremely thin.Therefore, the film thickness can easily be controlled and a problem ofscattering between elements can be solved.

Furthermore, in the present invention, a conductive inorganic compoundcontaining an element belonging to the II group in the periodic table isused to form the inorganic conductive layer; therefore, when the presentinvention is compared with cases in which an element belonging to the IIgroup in the periodic table is used as a single substance, diffusionthereof into the luminous element can be further reduced. Moreover, aluminous element having a strong resistance against deterioration due tooxygen can be formed since the inorganic compound has lower reactivitywith oxygen than the single substance.

1. A display device comprising: a cathode; a conductive layer comprisingan inorganic compound over the cathode; a light emitting layer over theconductive layer; an anode comprising a transparent conductive materialover the light emitting layer.
 2. A display device according to claim 1,wherein the conductive layer comprises a material having a smaller workfunction than the cathode.
 3. A display device according to claim 1,wherein the conductive layer comprises a material having an electricconductivity of 1×10⁻¹⁰ S/m or more.
 4. A display device according toclaim 1, wherein the inorganic compound is one of a boride and asilicate of an element selected from group II in the periodic table. 5.A display device according to claim 1, wherein the inorganic compound isone of a boride and a silicate of a rare earth element.
 6. A displaydevice according to claim 4, wherein the inorganic compound is selectedfrom the group consisting of magnesium boride, magnesium silicate,calcium silicate, strontium silicate, and barium silicate.
 7. A displaydevice according to claim 5, wherein the inorganic compound is selectedfrom the group consisting of yttrium boride and cerium boride.
 8. Adisplay device according to claim 1, wherein the inorganic compound isselected from the group consisting of calcium nitride, magnesiumnitride, calcium sulfide, magnesium sulfide, strontium sulfide, bariumsulfide, magnesium boride, magnesium silicate, calcium silicate,strontium silicate and barium silicate.
 9. A display device according toclaim 1, further comprising a thin film transistor, wherein the cathodeis electrically connected to the thin film transistor.
 10. A displaydevice according to claim 1, wherein the light emitting layer comprisesan organic material.
 11. A display device according to claim 1, furthercomprising an insulating film, wherein the insulating layer is formedover the cathode, and wherein the light emitting layer and the anode areformed over the insulating layer.
 12. A display device according toclaim 11, wherein the light emitting layer is in contact with theconductive layer.
 13. A luminous device according to claim 1, wherein awork function of the inorganic compound is 3.5 eV or smaller.
 14. Adevice according to claim 1, wherein the display device is incorporatedinto one selected from the group consisting of a display device, adigital still camera, a notebook-size personal computer, a mobilecomputer, a portable image-reproducing device having a recording medium,a goggle-type display, a video camera, and a portable telephone.
 15. Aluminous device comprising: an anode; a cathode; a light emitting layercomprising an organic compound provided between the anode and thecathode; and an inorganic conductive film comprising an inorganiccompound provided between the light emitting layer and the cathode andin contact with the cathode, wherein the inorganic compound comprises ametal element and a non-metal element, wherein the conductive filmcomprises a material having a smaller work function than the cathode andan electric conductivity of 1×10⁻¹⁰ S/m or more.
 16. A device accordingto claim 15, wherein the metal element is selected from group II in theperiodic table.
 17. A device according to claim 15, wherein theinorganic compound is a nitride, a sulfide, a boride or a silicatecomprising an element selected from group II in the periodic table. 18.A device according to claim 15, wherein the inorganic compound is amaterial selected from the group consisting of calcium nitride,magnesium nitride, calcium sulfide, magnesium sulfide, strontiumsulfide, barium sulfide, magnesium boride, magnesium silicate, calciumsilicate, strontium silicate and barium silicate.
 19. A device accordingto claim 15, wherein the luminous device is incorporated into oneselected from the group consisting of a display device, a digital stillcamera, a notebook-size personal computer, a mobile computer, a portableimage-reproducing device having a recording medium, a goggle-typedisplay, a video camera, and a portable telephone.
 20. A luminous devicecomprising: an anode; a cathode; a light emitting layer comprising anorganic compound provided between the anode and the cathode; and aninorganic conductive film comprising an inorganic compound providedbetween the light emitting layer and the cathode and in contact with thecathode, wherein the inorganic compound comprises a metal element and anon-metal element, wherein the conductive film comprises a materialhaving a work function of 3.5 eV or smaller and an electric conductivityof 1×10⁻¹⁰ S/m or more.
 21. A device according to claim 20, wherein themetal element is selected from group II in the periodic table.
 22. Adevice according to claim 20, wherein the inorganic compound is anitride, a sulfide, a boride or a silicate comprising an elementselected from group II in the periodic table.
 23. A device according toclaim 20, wherein the inorganic compound is a material selected from thegroup consisting of calcium nitride, magnesium nitride, calcium sulfide,magnesium sulfide, strontium sulfide, barium sulfide, magnesium boride,magnesium silicate, calcium silicate, strontium silicate and bariumsilicate.
 24. A device according to claim 20, wherein the luminousdevice is incorporated into one selected from the group consisting of adisplay device, a digital still camera, a notebook-size personalcomputer, a mobile computer, a portable image-reproducing device havinga recording medium, a goggle-type display, a video camera, and aportable telephone.